Speaking at the Liberal Party State Conference, Mr Turnbull was able to say he had delivered on a promise he made two years earlier of long-term GST reform for Western Australia.

"We knew the GST formula did not pass the pub test in Bunbury," Mr Turnbull said.

"But our job was to persuade Australians that it did not pass the pub test in Burnie or Bundaberg either."

A productivity commission inquiry, three separate cabinet meetings and close work between the treasurer and finance minister brought about the reforms.

The coalition's changes introduced GST payment benchmarks, according to the fiscal capacity of NSW or Victoria - whichever was the stronger.

"We've delivered a solution that ensures Western Australia receives not only its fair share, it ensures that injustice never happens again," Mr Turnbull said.

The speech wraps up Mr Turnbull's three-day visit to Perth, where he toured a small business in the seat of Swan on Thursday alongside MP Steve Irons.

On Friday, he was joined by Attorney-General Christian Porter as he visited the site of the $1.02 billion NorthLink project in the seat of Pearce.

The prime minister spent much of his time in Perth boasting about his government's solution to the GST revenue carve-up following years of frustration about WA's poor GST revenue share.

Planned changes to the tax formula would ensure WA receives no less than 75 cents per person for every dollar of GST raised in the state.

Mr Turnbull denied he was devoting time to both marginal seats because he was nervous about losing them at the next election.

Mr Porter said "of course" he was more confident about the next election following the GST announcement.

The prime minister has also dismissed questions about the Liberal party's decision to not contest the Fremantle and Perth by-elections, which Labor easily won.

He promised there would be a Liberal candidate for every seat at next year's federal election.

Australian Associated Press